(1) Field of the Invention
The present invention relates to a method of loading and locking tangential rotor blades and to a blade array having a new blade design.
(2) Prior Art
Gas turbine engines have a plurality of compressors arranged in flow series, a plurality of combustion chambers, and a plurality of turbines arranged in flow series. The compressors typically include at least a high pressure compressor and a low pressure compressor which are respectively driven by a high pressure turbine and a low pressure turbine. The compressors compress the air which has been drawn into the engine and provide the compressed air to the combustion chambers. Exhaust gases from the combustion chambers are received by the turbines which provide useful output power. Each compressor typically has a plurality of stages.
The main components of a typical tangential stage in a high pressure compressor are the disk, the blades, the ladder seals and the locks. FIG. 1 illustrates a cross section of the rear stages of a typical compressor. The blades 10 and the disk 12 are shown in FIG. 1. View X in FIG. 1 isolates the attachment portion of the disk 12. FIG. 2 shows the disk 12 with the loading slot 14 and the lock slots 16. FIG. 3 illustrates a top view of a ladder seal 18. FIG. 4 illustrates a cross section of the lock 20 and the disk 12.
The assembly sequence for a typical tangential stage is as follows. First, the ladder seal 18 is assembled to the inner rail of the disk 12 with a first slot 22 of the ladder seal 18 positioned directly over the loading slot 14 in the disk 12. Second, a first blade (not shown) is assembled through the ladder seal 18 and through the loading slot 14 in the disk 12. Then the blade and ladder seal 18 are rotated around the circumference of the disk 12 until the next slot 24 of the ladder seal 18 is positioned directly over the loading slot 14. In a similar fashion the next blade is loaded and rotated. Once the blades have been completely loaded and rotated in the ladder seal segment, the lock 20 is assembled through the load slot 14 and rotated to the lock slot position and tightened. The lock 20 prevents the circumferential motion of the blades, which insures that work will be done on the air and that the blades will not comeback out through the load slot.
Since locking and loading slots form discontinuities in tangential rotor disks, they have been known to initiate thermal mechanical fatigue (TMF) cracking. The root cause of any TMF cracking is the thermal gradients that exist at certain flight points. One flight point may produce a cold bore and a hot rim, which would put the rim (including the loading and locking slots) into compression. Another flight point may produce a hot bore and a cold rim which would put the rim into tension. This cyclic loading fatigues the disk. The locking and loading slots may make this condition worse by introducing stress concentrations due to the discontinuities.